PROJECT SUMMARY/ABSTRACT Autoimmunity in Systemic Lupus Erythematosus (SLE) is believed to be the result of a complex interplay between varying degrees of genetic susceptibility and environmental factors, which include pathogens and commensal gut microbes, dietary components and toxic substances. While recent studies, including ours, have shown much interest in understanding the role of interaction between environmental factors including gut microbes on autoimmunity, the potential contribution of inflammation initiated in the gut mucosa to systemic autoimmunity in lupus and the root cause of gut inflammation in lupus-susceptible background have not been investigated. This warrants studies to better understand the environmental and genetic factor interactions that trigger/perpetuate the early events of disease processes in at-risk subjects. Identification of early predictors of autoimmune processes will help develop novel, safe and effective strategies that can prevent systemic autoimmunity in lupus. Recently, using a spontaneous pre-clinical model of SLE which presents slow progressing disease and strong gender bias as seen in humans, we found that pro-inflammatory events are initiated in the gut mucosa at juvenile age (sex hormone independently), long before the onset of systemic autoimmunity and clinical disease, suggesting a role for these events in the systemic autoimmune process that occurs eventually. Our preliminary studies also identified previously unknown molecular events that cause gut inflammation and contribute to systemic autoimmunity. These studies show that 1) higher expression of X-linked TLR genes in intestinal epithelial and immune cells of lupus-prone females as early as juvenile age compared to lupus-resistant strain; 2) higher X- linked TLR expression and inflamed phenotype of gut mucosa at juvenile age positively correlates with the rate of autoimmune progression and disease incidence at late adult ages, 3) engagement of TLR7 and TLR8 induces profoundly high expression of inflammatory factors in IECs and immune cells from lupus-prone mice, and 4) depletion of gut microbiota suppresses gut inflammation and autoimmunity in them. These observations prompt us to hypothesize ?the systemic autoimmune process in lupus susceptible subjects is initiated and perpetuated, as gut inflammation at juvenile ages, by high-dose TLR7/8 - microbiota interaction?. Therefore, we propose studies: 1) to define the requirement of X-linked TLRs in gut inflammation and lupus autoimmunity; and 2) to determine the requirement of interaction with microbiota for, and the role of X-linked TLR activation in, juvenile onset of gut inflammation and lupus autoimmunity. Our proposed study is expected to identify early pro- inflammatory events that eventually lead to systemic autoimmunity in lupus, but also introduce a novel and rational therapeutic target for preventing lupus autoimmunity.